How is the dollars saved calculated?


#1

@bankstownbloke howdy, I was just wondering how the dollars Saved per day etc is calculated?


#2

Saved is -

  • Generation - Export, or
  • Consumption - Import

https://pvoutput.org/help.html#terms-definitions


#3

Cheers, Assuming I’m not misunderstanding the situation, (math was never my strong suit, I was wondering if the calculation should be something like:

Import Power costs avoided*, plus export earnings?

*in other words, what value is the power I self generated and used if it was imported from the grid during that period.


#4

Earnings (from exports x FIT) and Savings (from self consumption x import tariffs) is how I calculate it.

At least it’s indicative if not a true value for the financial benefit compared with not having solar PV.

It’s certainly fine way to calculate E&S if your tariffs are a flat rate.

With TOU tariffs it’s tricky as the timing of some discretionary loads would probably be altered if you didn’t have solar PV. e.g. If we didn’t have solar PV then I would swap our pool pump to be run largely during off-peak tariff times instead of daytime when solar PV is replacing peak and shoulder tariffs. So I’m not really saving as much as the above calculation might suggest since you’d change consumption patterns to suit the scenario. A true E&S would need to know when consumption would have occurred during each scenario, which is estimable but never really completely knowable.


#5

Good point, we do load shift our DW, Washing Machine & Dryer etc to utilise Solar generation hours but I still think this method that you have posted is the more accurate and logical way to calculate the savings.

Just to use my own case as an example, my power bill in the year prior to getting solar totaled $3,151 and in 2019 (first full year of solar) it’s going to be ~$1,600. That’s almost half, yet PVO calculates I’ve only “saved” $983 for this year so far and I wonder if the the logic used is really showing a true reflection of how much we are saving by having solar.


#6

Yeah, it’s just not really possible to precisely and accurately assess the earnings and savings of having solar. The good news is I would say the standard calculation method places a likely lower boundary on the probable E&S.

In my case the formulaic approach suggests my first full year E&S after solar was $2,646.

Like you, my pre and post solar bill impact is more than that.

Annual bill comparison for 2 years before and first year after Solar PV:

Average Bill Pre Solar: $4,745
Annual Bill Post Solar: $1,614
Annual Change in Bill: -$3,131

So that’s a $485 difference in the bill reduction.

That’s because there are various factors which influence the E&S results. One is using the data to make wiser choices about loads and load timing, another is using the data to make wiser choices about retail plans. Of course retail energy costs are not static either and sometimes retail plans with solar can be different to those without solar. Some might also choose to change how they heat water.